Sensei's Library - The "Wikipedia for Go," Sensei's Library is a community-edited website containing player guides, strategy articles, move and game analyses, and more.

KGS - The KGS Go Server - There are many places to play Go for free online, but KGS remains one of the most popular and easiest to use, for players of all levels. The easiest way to rapidly improve your Go playing skills is to play a quick game on KGS once a day!

Go Child - One great way to improve your ability to read situations on the Go board is to solve Go problems. "Go Child" lets you play through thousands of different problems for every skill level.

AGA - The America Go Association is the official national organization of American go players. They mantain a national rating system, organize the annual US Go Congress, assist local Go chapters, and organize touranments.

Books

The Second Book of Go - Richard Bozulich - Meant for players who've just learned the rules (their "first book" of Go), this is a great introduction for players who have very little experience and might otherwise feel overwhelmed by a more in-depth book.

Lessons in the Fundamentals of Go - Toshiro Kageyama - Inevitably the first book recommended for players who are serious about studying Go strategy and improving their skills. Kageyama's book can be revisited again and again as your skills improve, to continually glean new lessons.

The Elementary Go Series - Each book in the series focuses on a specific aspect of the game.

"Success at Go requires the tactic of the soldier, the exactness of the mathematician, the imagination of the artist, the inspiration of the poet, the calm of the philosopher, and the greatest intelligence."-Zhang Yunqi